The present invention broadly relates to an aqueous alkaline cleaning composition and process, and more particularly to a process employing an aqueous alkaline cleaner for cleaning aluminum container surfaces which are characterized by poor draining characteristics resulting in entrapment of the cleaning solution. The present invention is particularly adaptable for cleaning drawn and ironed aluminum container bodies of the types employed in the packaging of foodstuffs and beverages. The cup-shaped and dished integral bottom of such container bodies are conducive to entrapment of the cleaning solutions during processing which has resulted in an objectionable localized staining of the surfaces thereof during line stoppages during the cleaning cycle and prior to the subsequent water rinsing of the containers. Entrapment of the cleaning solution can also occur between cans at their points of contact while supported on the conveyor preventing satisfactory draining of the cleaning solution.
Line stoppages are a frequent occurrence in high-capacity, high-speed container washers the operation of which is integrated with other components of the container manufacturing line and may be occasioned, for example, by changeovers in the container decorating equipment as well as providing for periodic maintenance of sections of the production line. In any event, line stoppages ranging from about one-half minute to as long as about one hour frequently occur whereby the containers in the cleaning section of high-capacity, high-speed multiple stage washers are retained in the cleaning section for prolonged time periods having entrapped cleaning solution on at least portions of the surfaces thereof.
The localized etching evidenced by a white-etch staining of the surfaces of such containers occasioned by line stoppages is objectionable not only from an appearance standpoint but has also been found to detract from the adherence of subsequent sanitary lacquer coatings and decorative coatings applied to the container surfaces.
In addition to the aforementioned localized etching problem which produces a white staining on the surfaces of the container, a further problem has been encountered with respect to the surfactants or detergents employed which are necessary to remove the lubricants and other organic soils from the surface of the container body. It has been observed that surfactants heretofore employed have been deficient in many respects in preventing redeposition of such lubricants and organic soils on the cleaned container surface as the concentration of such lubricants and organics increases in the cleaning solution during prolonged usage. The redeposition of such organics on the container surface detracts from achieving optimum adherence of subsequently applied coatings to the container surfaces.
Still a further problem encountered when employing alkaline cleaners for cleaning aluminum container surfaces has been the tendency, in some instances, to produce a brown oxide stain or discoloration on the container surfaces during subsequent water rinsing of the cleaned container bodies. Such brown stains are objectionable not only from an appearance standpoint but also interfere in the attainment of optimum adherence of subsequently applied lacquer coatings.
A variety of aqueous alkaline cleaning compositions have heretofore been used or proposed for use for cleaning of substrates including glass containers and bottles. For example, U.S. Pat. No. 2,976,248 discloses an alkaline cleaner for glass jars employing an inhibitor to reduce corrosion of the mild steel conveyor belt employed in transferring the bottles through the washer mechanism; U.S. Pat. No. 4,147,652 discloses an alkaline cleaner concentrate also for cleaning glass bottles which is of relatively high alkalinity and optionally contains a chelating agent to prevent scale formation from hard water metal ions; U.S. Pat. No. 2,992,995 discloses a highly concentrated alkaline cleaner for cleaning superalloy engine parts to remove metal deposits therefrom; U.S. Pat. No. 3,779,933 discloses an alkaline oven cleaning composition which is highly concentrated and is devoid of any complexing agents while employing fatty acid soap ingredients unsuitable for use in accordance with the practice of the present invention; and U.S. Pat. No. 4,094,701 which discloses an alkaline cleaner for tin surfaces which is devoid of any complexing agents for the metal surface being cleaned. The foregoing prior art patents while generally applicable for cleaning substrates are directed to cleaning surfaces which are either insensitive to staining or discoloration such as glass, employ ingredients, and/or concentration of ingredients unsuitable for cleaning sensitive metal surfaces such as aluminum, or omit essential ingredients such as complexing agents which are necessary for use in the commercial practice of the present invention. U.S. Pat. No. 4,477,290 relates to an aqueous alkaline composition for cleaning aluminum containers which does not use or need surfactants and is unsuitable in practice as demonstrated by the tables in the Description of the Preferred Embodiment.
The process of the present invention overcomes the staining or localized discoloration problem of metal surfaces associated with prior art alkaline cleaners by incorporating a selected surfactant or combination of surfactants in further combination with conttrolled amounts of supplemental ingredients effecting an efficient and uniform cleaning of aluminum surfaces at relatively low temperatures while at the same time improving the flavor characteristics of the containers. The process for cleaning aluminum substrates in accordance with the present invention is further characterized by its versatility, flexibility, and ease of control and operation. At present, no alkaline cleaners have achieved commercial acceptance for use on aluminum containers.